Strongyloidiasis, also called threadworm infection, is a parasitic intestinal infection caused by the helminth Strongyloides stercoralis. This worldwide infection is endemic in the tropics and subtropics. Susceptibility to strongyloidiasis is universal. Infection doesn't confer immunity, and people who are immunocompromised may suffer overwhelming disseminated infection. Because the threadworm's reproductive cycle may continue in the untreated host for up to 45 years, autoinfection is highly probable. Most patients with strongyloidiasis recover, but debilitation from protein loss may result in death.
Transmission to humans usually occurs through contact with soil that contains infective S. stercoralis filariform larvae; such larvae develop from noninfective rhabdoid (rod-shaped) larvae in human feces. The filariform larvae penetrate the human skin, usually at the feet. They migrate by way of the lymphatic system to the bloodstream and the lungs.
Once they enter into pulmonary circulation, the filariform larvae break through the alveoli and migrate upward to the pharynx, where they are swallowed. They then lodge in the small intestine, where they deposit eggs that mature into noninfectious rhabdoid larvae. Next, these larvae migrate into the large intestine and are excreted in feces, starting the cycle again. The threadworm life cycle, which begins with penetration of the skin and ends with excretion of rhabdoid larvae, takes 17 days.
In autoinfection, rhabdoid larvae mature within the intestine to become infective filariform larvae.
The patient's resistance and the extent of infection determine the severity of symptoms. Some patients have no symptoms, but many develop an erythematous maculopapular rash at the site of penetration that produces swelling and pruritus and that may be confused with an insect bite. As the larvae migrate to the lungs, pulmonary signs develop, including minor hemorrhage, pneumonitis, and pneumonia; later, intestinal infection produces frequent, watery, and bloody diarrhea, accompanied by intermittent abdominal pain.
Severe infection can cause malnutrition from substantial fat and protein loss, anemia, and lesions resembling ulcerative colitis, all of which invite secondary bacterial infection. Ulcerated intestinal mucosa may lead to perforation and, possibly, potentially fatal dissemination, especially in patients with malignancy or immunodeficiency diseases or in those who receive immunosuppressants.
Diagnosis requires observation of S. stercoralis larvae in a fresh stool specimen (2 hours after excretion, rhabdoid larvae look like hookworm larvae). Duodenal aspirations show larvae present in duodenal fluid, and an antigen test that's positive for S. stercoralis. During the pulmonary phase, sputum shows S. stercoralis; marked eosinophilia also occurs in disseminated strongyloidiasis.
The goal of treatment is to eliminate the larvae with antithelmintics, such as ivermectin or thiabendazole. Patients may need protein replacement, blood transfusions, and I.V. fluids. Retreatment is necessary if S. stercoralis remains in stools after therapy.
❑Keep accurate intake and output records. Ask the dietary department to provide a high-protein diet. The patient may need tube feedings to increase caloric intake.
❑Use standard precautions when handling bedpans or giving perineal care, and dispose of feces promptly.
❑Because direct person-to-person transmission doesn’t occur, isolation isn’t required.
❑In pulmonary infection, reposition the patient frequently, encourage coughing and deep breathing, and administer oxygen as ordered.
❑To prevent reinfection, teach the patient proper hand-washing technique. Stress the importance of proper hand hygiene before eating and after defecating and of wearing shoes when in endemic areas. Check the patient's family and close contacts for signs of infection. Emphasize the need for follow-up stool examination, continuing for several weeks after treatment.
Review other book chapters online related to Strongyloidiasis:
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Professional Guide to Diseases (Eighth Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2005 ISBN: 1-58255-370-X 
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